Normal sinus rhythm of the heart begins with the sinoatrial node (or "SA node") generating an electrical impulse. The impulse usually propagates uniformly across the right and left atria and the atrial septum to the atrioventricular node (or "AV node"). This propagation causes the atria to contract.
The AV node regulates the propagation delay to the atrioventricular bundle (or "HIS" bundle). This coordination of the electrical activity of the heart causes atrial systole during ventricular diastole. This, in turn, improves the mechanical function of the heart.
Atrial geometry, atrial anisotropy, and histopathologic changes in the left or right atria can, alone or together, form anatomical obstacles. The obstacles can disrupt the normally uniform propagation of electrical impulses in the atria. These anatomical obstacles (called "conduction blocks) can cause the electrical impulse to degenerate into several circular wavelets that circulate about the obstacles. These wavelets, called "reentry circuits," disrupt the normally uniform activation of the left and right atria. Abnormal, irregular heart rhythm, called arrhythmia, results. This form of arrhythmia is called atrial fibrillation, which is a very prevalent form of arrhythmia.
Today, as many as 3 million Americans experience atrial fibrillation. These people experience an unpleasant, irregular heart beat. Because of a loss of atrioventricular synchrony, these people also suffer the consequences of impaired hemodynamics and loss of cardiac efficiency. They are more at risk of stroke and other thromboembolic complications because of loss of effective contraction and atrial stasis.
Treatment is available for atrial fibrillation. Still, the treatment is far from perfect.
For example, certain antiarrhythmic drugs, like quinidine and procainamide, can reduce both the incidence and the duration of atrial fibrillation episodes. Yet, these drugs often fail to maintain sinus rhythm in the patient.
Cardioactive drugs, like digitalis, Beta blockers, and calcium channel blockers, can also be given to control the ventricular response. However, many people are intolerant to such drugs.
Anticoagulant therapy also combat thromboembolic complications.
Still, these pharmacologic remedies often do not remedy the subjective symptoms associated with an irregular heartbeat. They also do not restore cardiac hemodynamics to normal and remove the risk of thromboembolism.
Many believe that the only way to really treat all three detrimental results of atrial fibrillation is to actively interrupt all the potential pathways for atrial reentry circuits.
James L. Cox, M. D. and his colleagues at Washington University (St. Louis, Mo.) have pioneered an open heart surgical procedure for treating atrial fibrillation, called the "maze procedure." The procedure makes a prescribed pattern of incisions to anatomically create a convoluted path, or maze, for electrical propagation within the left and right atria, therefore its name. The incisions direct the electrical impulse from the SA node along a specified route through all regions of both atria, causing uniform contraction required for normal atrial transport function. The incisions finally direct the impulse to the AV node to activate the ventricles, restoring normal atrioventricular synchrony. The incisions are also carefully placed to interrupt the conduction routes of the most common reentry circuits.
The maze procedure has been found very effective in curing atrial fibrillation. Yet, despite its considerable clinical success, the maze procedure is technically difficult to do. It requires open heart surgery and is very expensive. Because of these factors, only a few maze procedures are done each year.
One objective of the invention is to provide catheter-based ablation systems and methods providing beneficial therapeutic results without requiring invasive surgical procedures.
Another objective of the invention is to provide systems and methods that simplify the creation of complex lesions patterns in body tissue, such as in the heart.